Fig. 1: Crystal structures of bacterial STING in complex with c-di-GMP.

Surface and cartoon models of dimeric assembly of (a) PcSTING and (b) MySTING are presented with the two protomers colored differently. The bound c-di-GMP molecule is shown as a space-filled model. c The PcSTING (colored red–green–yellow) and MySTING (cyan–pink–magenta) protomers are superimposed and shown as cartoon models with the five α-helices and five β-strands indicated. d, e The Fo-Fc electron-density maps of the bound c-di-GMP molecules, each calculated by using the refined model with the ligand omitted, are contoured at 4-σ level and shown as mesh for the (d) PcSTING and (e) MySTING crystals. f The amino acid sequences of four known bacterial STING proteins are aligned based on their 3D structures. Residues interacting with the bound CDNs are indicated by yellow shade. The conserved RXR or RX(Y/F) motif in the β-strand lid which determines the ligand specificity is indicated by red arrows. The most involved residues in STING oligomerization as identified in this study are indicated by pink shade. CgSTING and FsSTING refer to the STING proteins from Capnocytophaga granulosa and Flavobacteriaceae sp.